Re: [PATCH v1] ACPI / scan: Acquire device_hotplug_lock in acpi_scan_init()

David Hildenbrand
2019-07-25T09:23:40Z

On 25.07.19 11:22, Rafael J. Wysocki wrote:
> On Thu, Jul 25, 2019 at 11:18 AM Oscar Salvador <osalvador@suse.de> wrote:
>>
>> On Wed, Jul 24, 2019 at 04:30:17PM +0200, David Hildenbrand wrote:
>>> We end up calling __add_memory() without the device hotplug lock held.
>>> (I used a local patch to assert in __add_memory() that the
>>> device_hotplug_lock is held - I might upstream that as well soon)
>>>
>>> [ 26.771684] create_memory_block_devices+0xa4/0x140
>>> [ 26.772952] add_memory_resource+0xde/0x200
>>> [ 26.773987] __add_memory+0x6e/0xa0
>>> [ 26.775161] acpi_memory_device_add+0x149/0x2b0
>>> [ 26.776263] acpi_bus_attach+0xf1/0x1f0
>>> [ 26.777247] acpi_bus_attach+0x66/0x1f0
>>> [ 26.778268] acpi_bus_attach+0x66/0x1f0
>>> [ 26.779073] acpi_bus_attach+0x66/0x1f0
>>> [ 26.780143] acpi_bus_scan+0x3e/0x90
>>> [ 26.780844] acpi_scan_init+0x109/0x257
>>> [ 26.781638] acpi_init+0x2ab/0x30d
>>> [ 26.782248] do_one_initcall+0x58/0x2cf
>>> [ 26.783181] kernel_init_freeable+0x1bd/0x247
>>> [ 26.784345] kernel_init+0x5/0xf1
>>> [ 26.785314] ret_from_fork+0x3a/0x50
>>>
>>> So perform the locking just like in acpi_device_hotplug().
>>>
>>> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
>>> Cc: Len Brown <lenb@kernel.org
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Oscar Salvador <osalvador@suse.de>
>>> Cc: Michal Hocko <mhocko@suse.com>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>
>> Given that that call comes from a __init function, so while booting, I wonder
>> how bad it is.
>
> Yes, it probably does not matter.

It can at least confuse lockdep, but I agree that this is not stable
material.

>
>> Anyway, let us be consistent:
>
> Right.
>

--

Thanks,

David / dhildenb